The present invention relates to projection optics, particularly to a projection optics assembly, and more particular to a projection optics box or assembly having a plurality of highly reflective optics located therein, with each optic being mounted to a precision actuator, for reflecting an image onto a point of use.
Optical lithography has provided the enabling technology to support the integrated circuit (IC) industry for several decades. However, new approaches will be required to maintain the projections for IC manufacturing after the turn of the century. One promising technology which builds on the optical experience is extreme ultraviolet lithography (EUVL) using 10 to 14 nm soft x-ray photons. For these wavelengths and 4x reduction, low numerical aperture (NA) imaging systems with printing resolutions less than 100 nm and a depth of focus (DOF) greater than 1.mu.are obtained. Technology scaling is expected to support several IC generations down to possibly 0.031 .mu.m. Because EUV photons are highly absorbed in essentially all materials and gases, special reflective optics contained in a vacuum environment are required to produce imaging.
EUV lithography has several advantages over other technologies. EUVL parallels and builds on the conventional optical lithography experience base: 1) imaging follows the relationships of conventional optics for resolution and DOF as a function of NA and is expected to scale down to 30 nm; 2) the robust 4x masks are easier to write than 1x, do not use fragile membrane, segmented masks and use conventional silicon processing to define the final geometric patterns on the mask; 3) the use of low NA optics provides good depth of focus for isolated and dense structures simultaneously, minimizing the need for mask biasing, 4) the technology provides a granular lithography tools solution for facility implementation when the laser produced plasma or other discrete source is used; 5) photoresists used currently are potentially extendible to EUV wavelengths; and 6) the technology is fully compatible with circuit design rules and could be introduced selectively at 0.13 .mu.m. In addition, the x-ray synchrotron sources may be used for EUVL with an appropriate condenser design.
Although technical progress in EUVL is being made, a number of challenges remain which must be addressed to assure the successful development of production equipment. These include: 1) continued improvement in EUV source efficiency and output power, 2) development of technical improvements and commercial sources for aspherical optics with adequate shape and finish, 3) optical coatings with maximum reflectivity at the selected wavelength which are stable with time, (4) projection optics for efficient imaging between the mask and the target or wafer, and 5) final integration of the entire system, complete with commercial mask and resist suppliers.
Substantial effort has been directed to development of aspherical optic utilizing highly reflective multilayer systems which reduce the stress on the substrate so as to obtain the desired shape and finish. These efforts are exemplified by U.S applications Ser. No. 09/027,308 filed Feb. 20, 1998, entitled "High Reflectance-Low Stress Mo-Si Multilayer Reflective Coatings", and Ser. No. 09/027,309 filed Feb. 20, 1998, entitled "Method-To Adjust Multilayer Film Stress Induced Deformation Of Optics", now U.S. Pat. No. 6,011,646 issued Jan. 4, 2000. Additional efforts to resolve the optics stress problem are exemplified by U.S. application Ser. No. 09/160,264, filed Sep. 25, 1998, entitled "Improved Method To Adjust Multilayer Film Stress Induced Deformation Of Optics"; U.S. application Ser. No. 09/157,116, filed Sep. 18, 1998, entitled "Post Deposition Method To Adjust The Reflectance Peak Position Of Extreme Ultraviolet Multilayer Mirrors"; and U.S. application Ser. No. 09/173,769, filed Oct. 16, 1998, entitled "Embedded Fiducials In Optics Surfaces" now U.S. Pat. No. 6,014,264 issued Jan. 1, 2000. Also, various efforts have been directed to the mounting of the optical components or mirrors, which are exemplified by U.S. application Ser. No. 09/098,693 filed Jun. 7, 1998, entitled "Precision Tip-Tilt-Piston Actuator That Provides Exact Constraint" now U.S. Pat. No. 5,986,827 issued Nov. 16, 1999; and U.S. application Ser. No. 09/164,414, filed Sep. 30, 1998, entitled "Pedestal Substrate For Coated Optics".
The present invention is directed to a solution of the above-identified challenge of providing efficient and effective projection optics between the mask and the target, such as a silicon wafer, of an EUVL system. The present invention involves a projection optics (PO) box or assembly positioned intermediate the mask and the target, and containing a plurality of optical components or mirrors, each being mounted on a precision actuator. In the illustrated embodiment four (4) optical components are utilized. the PO box is composed of a plurality of bulkheads secured together to form a unit construction of maximum rigidity. Three bulkheads are utilized in the illustrated embodiment.